1. Field of the Invention
The present invention relates to an original reader suitably used for a digital copier, a facsimile, an image scanner and so on, and more particularly to a scanning type original reader designed to read an image for each line of an original image.
2. Description of the Related Art
A variety of scanning type original readers designed to read an image for each line of an original image (e.g., Japanese Patent Laid-Open Nos. 9-284483, 10-79835, and so on) have heretofore been proposed.
FIG. 11 is a schematic view showing a conventional typical original reader; and FIG. 12 is a view showing a peripheral portion of a light source. This original reader comprises an imaging optical system, which includes a light source 1, a reflecting plate 2, mirrors 3a, 3b and 3c, and an imaging lens 4. By this imaging optical system, an original image of an original 6 set in an original reading position 5 is formed on a light-receiving surface of a line sensor (CCD) 7, and then the original image is read.
For the light source 1, a xenon lamp is generally used. The xenon lamp is constructed in such a manner that phosphor 8 is coated on a part of the inner wall surface of a glass tube 1A, rare gas mainly containing xenon gas is sealed in the tube, and a pair of strip electrodes (not shown) are provided in the outer wall of the glass tube 1A; and the lamp is lit by applying high-frequency voltages to the electrodes (Japanese Patent Laid-Open No. 3-225745 or the like).
The light source 1, the reflecting plate 2 and the mirror 3a are united to constitute a first mirror unit 9. Similarly, the mirrors 3b and 3c are united to constitute a second mirror unit 10. The first and second mirror units 9 and 10 are supported by a driving motor, a timing belt, and so on, not shown, so as to be freely moved in a direction parallel to a glass plate 11, that is, a direction of an arrow Y.
When the original reader reads the original 6 placed on the glass plate 11, the light source 1 is lit to irradiate the original reading position 5. In this case, ultraviolet rays 20 radiated from the light source 1 into the tube are converted into visible light 13 by the phosphor 8. After the visible light is radiated outside from an opening 1B of the glass tube 1A, the original reading position 5 is directly irradiated with a part of the visible light, and another part thereof is reflected by the reflecting plate 2 to irradiate the original reading position 5. In addition, the first and second mirror units 9 and 10 are simultaneously moved to the left in the drawing. In this case, in order to maintain a length of an optical path from the original reading position 5 to the line sensor 7 constant, a moving speed of the second mirror unit 10 is set to be half of that of the first mirror unit 9, and the second mirror unit 10 is moved by a distance half of a moving distance of the first mirror unit 9. Accordingly, the original reading position 5 is moved to the left by an amount equal to the moving amount of the first mirror unit 9, thereby forming an image of a new original reading position on the line sensor 7. As a result, by scanning the first mirror unit 9 only by an amount equal to the length of the original 6, it is possible to read the image of the entire original 6.
For the reflecting plate 2, an aluminum plate or the like, usually mirror finished, is used. By optimizing an opening angle A of the opening 1B of the light source 1, a direction X of the opening 1B, a sectional shape of the reflecting plate 2, and a position of the reflecting plate 2, illuminance at the original reading position 5 can be increased by about 1.5 times compared with the case of no reflecting plates 2 present.
FIG. 13 shows a peripheral portion of a light source of an original reader disclosed in the foregoing Japanese Patent Laid-Open No. 10-79835.
The original reader disclosed therein is designed to increase illumination efficiency and to reduce ultraviolet rays 20a harmful to the sensor in the following manner: the ultraviolet rays 20a radiated from the light source 1 and directly radiated outside of the glass tube 1A from the opening 1B of the light source 1 without being directed to the phosphor 8, are converted into visible light 13a by an illuminant 21 disposed outside the light source 1, and the original reading position 5 is irradiated with the visible light.
As described above, according to the conventional original reader shown in FIG. 13, the increase in illumination efficiency and the reduction in the ultraviolet rays 20a harmful to the sensor can be simultaneously achieved by converting the ultraviolet rays 20a directly radiated outside from the opening 1B of the light source 1, which are not directly usable for reading, into the visible light 13a by the illuminant 21. Thus, this original reader may be more advantageous than the conventional reader using the reflecting plate 2 shown in FIG. 11 and FIG. 12. However, since the illuminant 21 is disposed between the light source 1 and the glass plate 11, the light source 1 is located away from the original reading position 5, making it impossible to obtain a sufficient illumination effect. Thus, rather the conventional reader using the reflecting plate 2 shown in FIG. 12 may be more advantageous in terms of the illumination effect. However, since the reflecting plate 2 is provided without functions to convert the ultraviolet rays 20a into the visible light 13a, resulting in exerting a greater influence on the sensor, the use of the reader using the reflecting plate 2 is not recommended.